Dehydration of organic materials is commonly done in the food processing industry and in the production of biologically-active materials. It may be done in order to preserve the products for storage. It may also be done to create a product that is used in the dehydrated form, for example dried herbs and various kinds of chips. Conventional methods of dehydrating organic products include air-drying and freeze-drying. Both of these drying methods have their limitations. In general terms, air-drying is slow and freeze-drying is expensive, and both methods tend to degrade the appearance and texture of the products, which is undesirable in the case of foods.
Another method employed to dehydrate food products and biologically-active materials is microwave vacuum dehydration. Examples of this in the patent literature include WO 2009/049409 A1, Durance et al., published Apr. 23, 2009, and WO 2009/033285 A1, Durance et al., published Mar. 19, 2009. Microwave vacuum-drying is a rapid method that can yield products with improved quality compared to air-dried and freeze-dried products. Because the drying is done under reduced pressure, the boiling point of water and the oxygen content of the atmosphere are lowered, so food and medicinal components sensitive to oxidation and thermal degradation can be retained to a higher degree than by air-drying. The drying process is also much faster than air- and freeze-drying. The present invention is directed to improvements in the art of microwave vacuum-drying.